Ultrasonic Tweezers Research Articles

Acoustic black hole profiles for high-performance ultrasonic tweezers

Ultrasonic tweezers have provided significant capabilities for manipulating and handling objects in fluids across the fields of biomedical engineering, material preparation, micro/nano manufacturing, micro/nano robots, and so forth. However, most ultrasonic tweezers require precise design and professional operation, and an ultrasonic tweezer with more versatile, robust, and easy-to-use features is still scarce. In this study, through incorporating a one-dimensional acoustic black hole (ABH) structure, we propose and develop an innovative acoustic black hole tweezer (ABHT), which can easily realize multiple manipulation functionalities such as trapping of particles in various fluidic environments and cross-media extraction of particles. Numerical simulation results show that the ABH-enabled focused flexural waves at the tweezer’s tip can generate strong acoustofluidic effects including acoustic radiation forces on particles and acoustic streaming for particle trapping. We experimentally evaluate the performance of our ABHT, and also propose and demonstrate the topological device design with the high-throughput configurations. This work indicates that besides the conventional vibro-acoustic applications such as vibration mitigation and energy harvesting, ABHs can also play an effective role in ultrasonic particle manipulation devices. We believe the employment of ABHs would spur the emergence of more novel and useful ultrasonic particle manipulation and acoustofluidic devices in the future.

An Ultrasonic Tweezer With Multiple Manipulation Functions Based on the Double-Parabolic-Reflector Wave-Guided High-Power Ultrasonic Transducer.

The development of ultrasonic tweezers with multiple manipulation functions is challenging. In this work, multiple advanced manipulation functions are implemented for a single-probe-type ultrasonic tweezer with the double-parabolic-reflector wave-guided high-power ultrasonic transducer (DPLUS). Due to strong high-frequency (1.49 MHz) linear vibration at the manipulation probe's tip, which is excited by the DPLUS, the ultrasonic tweezer can capture microobjects in a noncontact mode and transport them freely above the substrate. The captured microobjects that adhere to the probe's tip in the low-frequency (154.4 kHz) working mode can be released by tuning the working frequency. The results of the finite-element method analyses indicate that the manipulations are caused by the acoustic radiation force.

Double parabolic reflectors wave-guided high-power ultrasonic transducer (DPLUS) based ultrasonic tweezers for micro/nano manipulation

Micro manipulation by ultrasonic technology has attracted wide attention recently due to its efficient manipulation process. In this work, Double Parabolic refLectors wave-guided high-power Ultrasonic tranSducer (DPLUS) which realized a low-loss and high-power ultrasound generation device was used as ultrasonic tweezers. The DPLUS can excite low (154.4 kHz) and high frequency (1.49 MHz) vibration modes, which can achieve two kinds of micro/nano multi manipulation modes in water. In this study, the axially vibrating needle of DPLUS was vertically immersed into the droplet to manipulate micro/nano samples including copper wire, TiO2 powders and yeast cells.

A new strategy to capture single biological micro particles at the interface between a water film and substrate by ultrasonic tweezers

Controlled capture of single biological micro particles, with effective capture function, little heat damage to and good stability of captured samples simultaneously, has been a technological challenge in the area of micro manipulation. This paper presents an ultrasonic tweezers based new strategy to meet the challenge. In the strategy, being different from the other ultrasonic methods, the MMP (micro manipulating probe), which vibrates elliptically, is in contact with the substrate. Single yeast cells with a diameter of 3–7 μm and Chlorella vulgaris powders with a diameter of 2–10 μm near the MMP can be sucked onto the MMP’s tip. The captured particle can be transferred to a desired location at the interface between the water film and substrate by moving the ultrasonic tweezers. The temperature rise in the capture region is less than 0.1 °C, and the sucking distance can be up to 20 μm. The captured particle is in contact with the MMP’s tip, which results in a good stability of the captured particle. The experiments also show that it is possible to use multiple MMPs to individually capture single cells. The finite element analyses indicate that acoustic radiation force generated by the ultrasonic field around the MMP is responsible for the capture. Moreover, the effects of the orthogonal vibration components, tilt angle and length of the MMP on the capture capability are clarified.

High-Performance Ultrasonic Tweezers for Manipulation of Motile and Still Single Cells in a Droplet

The manipulation of motile and still single cells with the simultaneous features of selective trapping, 3-D path free transport, position-controllable release and little heat damage has been a significant challenge. We developed an ultrasonic method for capturing motile and still single cells with the aforementioned features in a droplet. During manipulation, a micromanipulation probe (MMP), which vibrated linearly with a trajectory parallel to a silicon substrate, was immersed in the droplet and was not in contact with the substrate. Motile and still single cells, such as Chattonella marina with a length of 30–50 μm and yeast cells with a diameter of 3–10 μm, at the interface between the droplet and substrate were selectively sucked onto the vibrating MMP and transported via a 3-D route inside the droplet by moving the MMP (or the device). The MMP and captured single cells were in contact, making the release position controllable. The measured temperature rise of the MMP was <0.1°C; thus, it is competitive for the manipulation of biological samples. Finite-element analyses revealed that the contact-type capture was due to acoustic radiation force generated by the ultrasonic field around the vibrating MMP. The dependence of the capture capability and working frequency bandwidth on the working conditions was investigated experimentally.

Capture of Individual Micrometal Wires in Air by Ultrasonic Tweezers

In this paper, a strategy to capture individual micrometal wires in air by ultrasound is demonstrated. Curved and flattened tip of a vibrating needle excited by a sandwich-type transducer, operating at about 45.8 kHz, is employed to capture micrometal wires in air. A 40-μm-diameter copper wire with a length of 1–14 mm can be trapped stably by ultrasound and transferred through any 3-D path in air by moving the transducer. The trapping is caused by the acoustic radiation force. The trapping capability, which is defined by the maximum length of a trapped micrometal wire, increases with the increase of the needle vibration, and decreases when the needle vibration is too large. Decreasing the manipulating edge's thickness of the needle's tip and selecting proper material for the needle can enhance the trapping capacity. The shape of the needle's tip also influences the trapping capacity. The manipulating tip has a temperature rise up to 38.5°C to trap the 40-μm-diameter copper wires with a length of 1–14 mm.

Patterning of microspheres and microbubbles in an acoustic tweezers

We describe the construction of an ultrasonic device capable of micro-patterning a range of microscopic particles for bioengineering applications such as targeted drug delivery. The device is formed from seven ultrasonic transducers positioned around a heptagonal cavity. By exciting two or three transducers simultaneously, lines or hexagonal shapes can be formed with microspheres, emulsions and microbubbles. Furthermore, phase control of the transducers allows patterning at any desired position in a controlled manner. The paper discusses in detail direct positioning of functionalised microspheres, emulsions and microbubbles. With the advantages of miniaturization, rapid and simple fabrication, ultrasonic tweezers is a potentially useful tool in many biomedical applications.

A /spl pi/-shaped ultrasonic tweezers concept for manipulation of small particles

A pi-shaped ultrasonic actuator is proposed for the noncontact trapping, extraction, and transportation of small particles. In this actuator, two metal plates clamp a multilayer piezoelectric vibrator by a small bolt, and the metal plates are tapered in their lower parts so that a vibration gradient can be obtained. The flexural vibration of the metal plates is used to generate a sound field in the gap between the two tapered metal plates. At a driving frequency of about 152.8 kHz, shrimp eggs, grass seeds, thyme seeds, rice powder, fine salt, and fine sugar, which have an average diameter from several tens of micrometers to several hundreds of micrometers, can be trapped stably without contact with the actuator, and the particles insoluble in water can be extracted from water and transported in water by the actuator. In the noncontact trapping of small particles, the positions of trapped particles as well as the relationship among the number of trapped particles, vibration velocity, and input power are investigated. The number of trapped particles increases as the vibration velocity or input power increases. However, when the vibration velocity or input power is too large, the particles may be ejected out of the actuator and, therefore, cannot be stably trapped. The minimum vibration velocity to trap small particles increases as particle density increases for the particles that have the shape near to a sphere and a proper density. In the extraction of small particles from water, the relationship between the number of extracted thyme seeds and the input power is investigated. Increasing the input power can increase the extracted thyme seeds. However, there is a maximum particle number that can be extracted from water. In the transportation of thyme seeds in water, the dependence of the particle loss during the transportation on the speed and distance of transportation and the input power is experimentally estimated. As the distance and speed of transportation increase, the particle loss during the transportation increases. Increasing the input power increases the trapping effect and, therefore, decreases the particle loss.